Further studies on acclimatization to low temperatures in the grain weevils Sitophilus oryzae (L.) and Sitophilus granarius (L.)

The effect of thermal acclimatization on the resting metabolism of adult grain weevils was examined by closely restraining the weevils during respirometry. Sitophilus oryzae (L.) acclimatized to 15°C consumed less oxygen over 11–23°C than 27°C-acclimatized weevils but like amounts over 25–35°C. Similar results were observed with S. granarius (L.). Respiration R–T curves of unrestrained S. oryzae and S. granarius showed no evidence of rotation at temperatures close to their chill-coma thresholds but warm- and cold-acclimatized weevils consumed similar amounts of oxygen when both categories of weevils were in chillcoma. Acclimatizing S. oryzae from 27 to 13.5°C through four, weekly 4.5°C step-transfers lowered the median chill-coma thresholds of the weevils from 8.9 to 6.2°C, increased their life span at 9°C, an unfavourable temperature for this species, from 2 to 8 weeks and lowered their oxygen uptake at 9°C by 19%.     

The capacity for increase at a low temperature of several Australian populations of Sitophilus oryzae (L.)

The capacity for increase (I_c) of one laboratory and seven field populations of young adult S. oryzae from different sites in Australia was determined over a thirty-week period at 15°C, a supposedly marginal temperature, in wheat of 14% moisture content. The average value of I_c was 0.0838 ± 0.0017 and the populations comprised three significantly different groups. Variations in the net rate of increase per generation (R₀) which averaged 34.7±1.71, had a major effect on the value of r_c whereas variation in the cohort generation time (T_c), which averaged 41.6±.23 weeks had only a minor effect. The survivorship of adults of the populations did not differ significantly and 93% of females were alive after thirty weeks. Estimates of r_c based on a fifteen-week period and on an amended value of Tc differed little from those over thirty weeks. The capacity for increase at 15°C of a given population was found to be correlated with its fertility at 27°C and with its body-weight rather than with its cold-tolerance, as evidenced by chill-coma temperature, or with its previous temperature-history. The temperature experienced by the immature stages of weevils had a profound effect on r_c in that weevils reared at 15 and 27°C had respective values of 0.0350 and 0.0707 when subsequently cultured at 15°C. Because all observed values of r_c were higher than expected, possible errors in method were considered. An alternative estimate of R₀ agreed closely with that observed and indicated that only 17% of the immature stages survived at 15°C. Metabolic heating due to the higher than expected population density shortened the duration of the immature stages by 7% but did not affect their survival.     

Inheritance and Characterization of Strong Resistance to Phosphine in Sitophilus oryzae (L.)

Sitophilus oryzae (Linnaeus) is a major pest of stored grain across Southeast Asia and is of increasing concern in other regions due to the advent of strong resistance to phosphine, the fumigant used to protect stored grain from pest insects. We investigated the inheritance of genes controlling resistance to phosphine in a strongly resistant S. oryzae strain (NNSO7525) collected in Australia and find that the trait is autosomally inherited and incompletely recessive with a degree of dominance of -0.66. The strongly resistant strain has an LC50 52 times greater than a susceptible reference strain (LS2) and 9 times greater than a weakly resistant strain (QSO335). Analysis of F2 and backcross progeny indicates that two or more genes are responsible for strong resistance, and that one of these genes, designated So_rph1, not only contributes to strong resistance, but is also responsible for the weak resistance phenotype of strain QSO335. These results demonstrate that the genetic mechanism of phosphine resistance in S. oryzae is similar to that of other stored product insect pests. A unique observation is that a subset of the progeny of an F1 backcross generation are more strongly resistant to phosphine than the parental strongly resistant strain, which may be caused by multiple alleles of one of the resistance genes.     

Some aspects of acclimation to low temperatures in the grain weevils Sitophilus oryzae (L.) and S. granarius (L.)

The ability of Sitophilus oryzae (L.) and S. granarius (L.) to acclimate when transferred from 27°C, a near optimal temperature, to 15° C, a marginal temperature, was examined in terms of chill-coma temperature, dispersal, oxygen consumption and rate of oviposition. The chill-coma temperature of S. oryzae was higher and the increment of acclimation less than that of S. granarius. Acclimation, although well advanced after 2 weeks after transfer, took more than 4 weeks to complete. Re-acclimation after the reciprocal transfer took only 2 weeks. The dispersal of S. oryzae held at 15 and 27° C prior to testing differed when the weevils were released in wheat at 27°C but not when released at 15°C. Cold-acclimated S. granarius dispersed less than warm-acclimated weevils when released in wheat at both 15 and 27°C. The activity oxygen consumption of cold-acclimated weevils was less than that of warm-acclimated weevils. Inverse-shifts of acutely determined R-T relationships appeared more significant than changes in temperature sensitivity. Acclimation to 15° C took 8–10 days and re-acclimation to 27°C about 6–8 days. S. oryzae consumed less oxygen per unit of weight than S. granarius but was more temperature sensitive. Resting oxygen consumption, which was less temperature sensitive than activity consumption, also exhibited inverse acclimation in both species. S. granarius showed evidence of inverse acclimation of oviposition rate after acclimation at 15°C.     

A comparison of the capacity for increase at a low temperature of foreign and Australian populations of Sitophilus oryzae (L.) and S. granarius (L.)

The capacity for increase (r_c) of three populations of S. oryzae and three populations of S. granarius from Great Britain and Canada was determined over 15 and 24 weeks respectively at 15°C in wheat of 14% moisture content. The fertility of these populations at 27°C, their body weight and chill-coma threshold was also measured. With both S. oryzae and S. granarius, values of r_c for the foreign populations fell within the range previously observed when several Australian populations were reared under the same conditions. The cohort generation times (T_c) of the foreign S. oryzae populations were significantly shorter than those of the Australian populations because of the shorter immature development periods (D) of the former. Two of the foreign S. granarius populations had lower values for D than all but one of their Australian counterparts but their values of T_c were within the range previously observed for Australian weevils. When the Australian and foreign populations were considered together, the value of r_c was more strongly correlated with fertility at 27°, an optimal temperature, than with body weight in both S. oryzae and S. granarius. With S. oryzae, r_c was correlated with the chill-coma threshold of cold-acclimated weevils only. There were no correlations between r_c and chill-coma thresholds in S. granarius. It was concluded that the observed differences in r_c were related to differences in the vigour of the populations rather than to physiological differences in cold-tolerance. The likelihood of grain weevils becoming cold-tolerant as a result of grain aeration is discussed and the practical significance of differences in r_c considered.     

Pectin methylesterase from the rice weevil,Sitophilus oryzae (L.) (Coleoptera: Curculionidae): Purification and characterization

A pectin methylesterase was purified to apparent homogeneity from the adult rice weevil, Sitophilus oryzae (L.), by Q-Sepharose and S-Sepharose chromatographies followed by high-performance anion-exchange chromatography. The resulting preparation is the first pectin methylesterase which has been purified from any animal species, although at this point we cannot rule out the possibility that the enzyme is produced by a symbiotic microorganism. The molecular mass of the enzyme was estimated as 38 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This mass is similar to those of pectin methylesterases previously isolated from bacteria, fungi, and plants. The purified enzyme had a broad pH optimum between 6 and 7, which appears consistent with the enzyme's probable site of action, the gut.     

饲养密度对洋虫生长发育的影响

在30℃下,研究了饲养密度对洋虫Palembus dermestoides(Fairmaire)幼虫生长发育的影响,并用Weibull频数分布函数探讨了饲养密度对洋虫幼虫存活率的变动影响。结果表明:饲养密度对幼虫存活率影响明显,存活曲线均属于Ⅰ型;但对幼虫体重增长的影响并不显著,饲养密度以0.51~1.53头/cm2为宜,密度过低或过高都使幼虫存活率下降、历期延长,在低密度下幼虫化蛹后的蛹较重,更适合种群的繁衍。     

Lethal and sublethal effects of rice polishing process on Sitophilus oryzae (Coleoptera: Curculionidae)

The mechanical impact of rice polishingon the rice weevil, Sitophilus oryzae (L.), and the subsequent postpolishing effects associated with rice quality were studied. "Brown" rice (not polished), "White (infest then polish)" rice, and "White (polish then infest)" rice were used with different polishing process intensities and different initial weevil densities. Weevil progeny were more numerous in Brown than in White (infest then polish) or White (polish then infest) rice. Polishing corresponding to a weight loss of 11% in rice generated an immediate mortality of approximately 40%; the subsequent mortality caused by rice quality was also 40% (total >80%). A polishing process corresponding to 14 and 16% of rice weight loss generated a drastic mortality in the weevil population (>95%). The progeny per adult weevil was similar with high and low initial weevil densities. The development of weevil progeny was also delayed by about 1 wk in White (infest then polish) rice compared with Brown rice. Furthermore, weevil adults of the progeny were significantly heavier in Brown than in White (infest then polish) or White (polish then infest) rice.     

Scanning electron microscopy of the spermatheca in Sitophilus granarius (L.)

With scanning electron microscopy the spermathecal organ of Sitophilus granarius (L.) has been examined. The only morphological attachment between this organ and other tissues is to the bursa copulatrix by the sperm duct and to the central nervous system by two nerve fibers. The nerves innervate the muscles connecting the two arms of the U-shaped spermatheca. Glandular cells are grouped together and are connected to the spermathecal lumen by a short collecting duct. Vascular sinuses opening from the body cavity into the body of the gland are observed as pores on the surface of the gland.     

Cytochrome c oxidase inhibition in the rice weevil Sitophilus oryzae (L.) by formate, the toxic metabolite of volatile alkyl formates

Volatile alkyl formates are potential replacements for the ozone-depleting fumigant, methyl bromide, as postharvest insecticides and here we have investigated their mode of insecticidal action. Firstly, a range of alkyl esters, ethanol and formic acid were tested in mortality bioassays with adults of the rice weevil, Sitophilus oryzae (L.) and the grain borer, Rhyzopertha dominica (F.) to determine whether the intact ester or one of its components was the toxic moiety. Volatile alkyl formates and formic acid caused similar levels of mortality (LC(50) 131-165 micromol l(-1)) to S. oryzae and were more potent than non-formate containing alkyl esters and ethanol (LC(50)>275 micromol l(-1)). The order of potency was the same in R. dominica. Ethyl formate was rapidly metabolised in vitro to formic acid when incubated with insect homogenates, presumably through the action of esterases. S. oryzae and R. dominica fumigated with a lethal dose of ethyl formate had eight and 17-fold higher concentrations of formic acid, respectively, in their bodies than untreated controls. When tested against isolated mitochondria from S. oryzae, alkyl esters, alcohols, acetate and propionate salts were not inhibitory towards cytochrome c oxidase (EC 1.9.3.1), but sodium cyanide and sodium formate were inhibitory with IC(50) values of 0.0015 mM and 59 mM, respectively. Volatile formate esters were more toxic than other alkyl esters, and this was found to be due, at least in part, to their hydrolysis to formic acid and its inhibition of cytochrome c oxidase.     

In vitro propagation of caper (Capparis spinosa L.)

Summary A twenty fold multiplication per twenty days of caper was achieved by culturing nodal shoot segments in the presence of BAP (4 μM) plus IAA (0.3 μM) and GA₃ (0.3 μM). The use of a modified MS medium facilitated this response. Plantlet regeneration was induced on single shoots taken from proliferating clusters subcultured for 20 days on a reduced BAP (2 μM) without auxin and gibberellin Higher rooting responses (70%) were obtained after a 20-day incubation period in darkness on solid half-strength MS1 medium plus IAA (30 μM), followed by a subsequent 20 day culture period on half-strength MSI basal medium. Proliferation was mainly due to axillary shoot-bud development as revealed by histological studies. The extensive meristematic activities observed indicated the enormous morphological potential of this species.     

In vitro culture ofBellevalia romana (L.) Rchb.

Summary Bellevalia romana (L.) Rchb., a monocotyledonous plant characterized by few (2 n=2 x=8) and very large chromosomes, is a useful subject for studying developmental problemsin vitro. Cytological analysis of callus revealed that the majority of cells were diploid, but the remaining cells had aneuploid nuclei with a wide range of chromosome numbers, tetraploid and haploid nuclei. The frequency of aneuploid and polyploid cells was higher in callus grown in the presence of 2,4-D than in callus grown in NAA plus BAP. These nuclei seemed to increase with the duration of culture. The chromosome number distribution as determined by chromosome counts in calli at different culture times was confirmed by DNA cytophotometry. Chromosome number mosaicism (mixoploidy and aneusomaty) also occurred in all root apices of 9 out of 46 plantlets regenerated from callusvia adventitious shoots.     

Effectiveness of monoterpenes and phenylpropenes on Sitophilus oryzae L. (Coleoptera: Curculionidae) in stored wheat

Six monoterpenes, ((?)-citronellal, p-cymene, (?)-menthone, α-pinene, α-terpinene and (?)-terpinen-4-ol) and two phenylpropenes, (trans-cinnamaldehyde and eugenol) were tested for their insecticidal activity against the rice weevil, Sitophilus oryzae under laboratory conditions. The bioassays were carried out on wheat at the concentrations of 0.5, 1.0 and 5.0?g/kg. Adult mortality was assessed after 14?days of exposure. After this interval, the treated wheat was retained for an additional period of 90?days, in order to evaluate progeny production and wheat loss. At the concentrations of 0.5 and 1.0?g/kg, trans-cinnamaldehyde and eugenol achieved highest adult mortality. At 5.0?g/kg, all compounds except for p-cymene and α-pinene caused complete (100%) adult mortality. Generally, trans-cinnamaldehyde was the most potent compound causing complete inhibition of progeny at the three concentrations. Similarly, no progeny were observed in the wheat treated with (?)-citronellal, eugenol, p-cymene, (?)-menthone, and (?)-terpinen-4-ol at 5.0?g/kg after 45 and 90?days. Similar trends were noted for wheat weight loss and damage as the treatment with monoterpenes and phenylpropenes at the highest rate preserved the wheat intact and free from damage by S. oryzae for 90?days. Our findings suggest the tested compounds except p-cymene and α-pinene could be recommended for use as part of an integrated pest management program for S. oryzae control in stored wheat.     

In vitro studies on Pea (Pisum sativum L.): I. Callus formation,regeneration and rooting

Abstract

Callus production, shoot formation via organogenesis and rooting of the regenerated shoots are reported in an Egyptian variety of Pisum sativum L. Calli were initiated from hypocotyl, leaf, root and mature embryo explants when cultured on MS medium containing B5 vitamins and supplemented with 2 mg/l 2,4-D+1 mg/l kin. Among the different types of explants, hypocotyl showed best potential for callus proliferation. Hypocotyl, leaf and immature cotyledon explants were used for shoot organogenesis. The best results of shoot formation were achieved when hypocotyl explants were cultured on MS-medium supplemented with 2 mg/l BA+1 mg/l NAA. However, immature cotyledon explants showed the highest frequency of shoot formation with 1 mg/l BA. Data of in vitro rooting showed that maximum root frequency occurred on culture medium containing half strength of MS salts, 40 g/l sucrose and 2 mg/l NAA.